Cutter Compensation

Cutter Compensation

Cutter compensation explained.

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This is a video explaining cutter compensation in CNC programming.

You will come across various terms to describe this such as:

  •  Tool cutter comp.
  •  CNC cutter comp.
  •  G41 G42 cutter compensation.
  •  Cutter diameter compensation.
  •  Cutter radius compensation.
  •  Heidenhain RL RR.

Cutter compensation is referred to as cutter diameter compensation and cutter radius compensation

Haas cutter compensation, Fanuc cutter compensation and Mazak cutter compensation all work in the same way.

Although Heidenhain cutter compensation or Heidenhain cutter comp looks different. In the programme it functions in exactly the same way.

Cutter Compensation

In the parameters or settings of your control you can set up your system to use the radius or the diameter of your cutting tool.

This means that when you input the data for your cutting tool in your offset table you can use the diameter or the radius of the tool.  This depends on your settings.

Cutter Compensation

When people talk about cutter compensation G code they may say “cutter comp G code” it’s often shortened.
(Cutter compensation G code)
The G codes used in this video are:

  •  G41 cutter compensation left
  •  G42 cutter compensation right
  •  G40 G code to cancel cutter compensation

This Video shows you :

  • How to program G41.
  • How to program G42.
  • CNC cutter compensation examples.
  • Cutter compensation Heidenhain style.
  • Heidenhain RL RR.

We always recommend that you climb mill so you will be using G41 most of the time.

Milling the outside of a square using G41.

Cutter Compensation

Milling the inside of a square using G41.

Cutter Compensation

Milling the inside of a square using G42 (should you want to conventional mill).

Cutter Compensation

Milling the outside of a square using G42 (should you want to conventional mill)

Cutter Compensation


The rules when using compensation on a CNC Milling machine.

Rules are the same as the tool nose radius compensation on a CNC Lathe.
If you programme a shape and you do not use cutter compensation you will have to work out the size of the shape with your tool radius added.

This is simple on a square sided figure or a simple radius. Anything more complex and it’s a nightmare.
I just heard some smart arse say “Ah well my CAD system takes care of that”.
So it should my friend but, and there is a but:

  • What will you do when your cutter wears?
  • What if you want to use a different size cutter?
  • The cutter may not run true.
  • What if the cutter is not exactly size?

In the old days of paper tape and Corned Beef we as programmers would write several programmes.

This was so that we could re-grind the milling cutters in fixed increments. A different programme could be used each time the tool was changed.

Sorry I can’t talk about this much longer as I still have the nightmares (mainly about corned beef sandwiches).

Cutter Compensation


Anyway enough of that. So when we machine our first profile we can add some on to the tool radius in the offset file. When we check the part we can adjust the offset and re-cut the profile to achieve an accurate result.

The Rules:

  • Shape must be continuous and consistent.
  • You can’t cut along a line and then go back along it.
  • It’s important to allow more than the tool radius when entering tool compensation. The same applies when you come out of tool compensation.
  • Internal corner radii and steps must be greater than the tool radius.

Always allow more than the radius because when you adjust it it may be larger than the actual tool you are using.

Don’t ask

For example if you have a 12mm endmill but you have .2mm in the wear compensation. The machine thinks that the tool is 12.4mm in diameter.

You can’t do this in cutter comp:

Cutter Compensation

You would have to apply one cut in G41 and cancel with G40 then do another cut in G42 and cancel with G40:

Cutter Compensation

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